Mesoscale Precipitation Discussion 0384
NWS Weather Prediction Center College Park MD
1158 PM EDT Thu Jun 06 2019
Areas affected...Northeast MS...Central/Northern AL
Concerning...Heavy rainfall...Flash flooding possible
Valid 070355Z - 070900Z
SUMMARY...Showers and thunderstorms with very heavy rainfall rates
are expected over the next several hours. Some flash flooding will
be possible.
DISCUSSION...The latest radar imagery is showing an axis of
showers and thunderstorms advancing through portions of
east-central/northeast MS and central AL as an area of low
pressure lifts northeast across northern MS. The low center is
embedded along a quasi-stationary frontal zone, and is
facilitating a broad warm air advection pattern across much of the
Gulf Coast region in conjunction with deeper layer southwest flow
ahead of an upper trough and associated closed low moving into the
lower MS Valley region.
A reasonably broad area of larger scale isentropic ascent is
already in place across much of the region as a result of the
deeper layer southwest flow, but it is expected that this ascent
will tend to strengthen a bit overnight as stronger height falls
and southwest flow encroach on the region. This will allow the
front to begin to lift northward as a warm front and is expected
to help maintain a focus for at least broken areas of showers and
thunderstorms. Additionally, the region is beginning to feel the
impacts of a well-defined upper-level jet streak advancing east
across northern LA and west-central MS, with improving downstream
left-exit region upper-level jet dynamics. This enhanced jet
energy is helping to strengthen the ongoing clusters of
convection, and over the last hour there has been some substantial
cooling of the convective tops which is indicative of stronger
forcing and resulting updrafts. This is all occurring also within
an extremely moist and at least modestly unstable environment
characterized by PWATS of 2.0 to 2.2 inches and MUCAPE values of
around 1000 j/kg at least in vicinity of the front.
The very moist environment coupled with the arrival of stronger
forcing is allowing for rainfall rates to become quite extreme
with some of the colder cloud-topped convection, and the latest
dual-pol radar QPE is suggesting hourly rainfall amounts of as
much as 3+ inches/hr with a focus most recently on Lowndes county
in northeast MS.
Expect some additional expansion of convection over the next
couple of hours with very heavy rainfall potential across portions
of especially northeast MS and northern AL. The 00Z HREF suite of
guidance suggests at least locally the threat of 3 to 5 inches of
rain going through 09Z, but this will tend to be with the stronger
convective cores. On a broader scale, the potential will tend to
be on the order of as much as 2 to 3 inches. However, given such
high rainfall rates in just a 1 to 2 hour time frame, the area FFG
values are expected to be locally exceeded and thus flash flooding
will be possible